The present invention relates to a process for preparing N,N-substituted 3-aminopropan-1-ols.
The preparation of N,N-substituted 3-aminopropan-1-ols is disclosed, for example, in European patent application EP-A1-0673918. N,N-substituted 3-aminopropan-1-ols are obtained by converting ethylene cyanohydrin and secondary amines over a palladium catalyst at elevated temperatures and pressures.
EP-A2-0869113 discloses the preparation of N,N-substituted 3-aminopropan-1-ols from ethylene cyanohydrin and secondary amines, such as dimethylamine, the reaction being performed at temperatures of 50 to 250° C., a pressure of 5 to 350 bar, in the presence of a palladium-comprising catalyst. The supported catalyst used comprises 0.1 to 10% by weight of palladium, based on the total weight of the catalyst, and at least one further metal selected from groups IB and VIII of the Periodic Table, cerium and lanthanum.
It was an object of the present invention to provide a process for preparing N,N-substituted 3-aminopropan-1-ols from acrolein. More particularly, it was an aim of the present invention to provide a new preparation route for industrially important N,N-substituted 3-aminopropan-1-ols, such as N,N-dimethyl-3-aminopropan-1-ol (DMAPOL), in which feedstocks which can be obtained on the basis of renewable raw materials are used. Acrolein can be prepared, for example, by dehydrating glycerol, which in turn can be obtained as a by-product from fat hydrolysis or biodiesel production. The use of renewable resources in the preparation of such products can contribute to preservation of petrochemical resources which are typically used. A further intention was to provide a process for preparing N,N-substituted 3-aminopropan-1-ols, in which N,N-substituted 3-aminopropan-1-ols are formed in high yield and high selectivity, and which is additionally technically easy to handle and has a high level of process economy.
The reaction of acrolein with secondary amines has already been described in DE-A-4232424 and by Finch et al. (H. D. Finch, E. A. Peterson and S. A. Ballard, J. Am. Chem. Soc., 74, 2016 (1952)).
In DE-A-4232424, from 2-alkenals and secondary amines, the corresponding N,N,N′,N′-substituted unsaturated amines are obtained, which can be hydrogenated in a further reaction to the saturated amines. There is no indication that reaction of acrolein with secondary amines and subsequent hydrogenation can provide N,N-substituted 3-aminopropan-1-ols with high selectivity.
Finch et al. (H. D. Finch, E. A. Peterson and S. A. Ballard, J. Am. Chem. Soc., 74, 2016 (1952)) describe the reaction of acrolein or methacrolein with primary or secondary amines. The N,N′-substituted 1,3-propenediamines or N,N,N′,N′-substituted 1,3-propenediamines thus obtained are, according to the disclosure, hydrogenated in a next stage to the corresponding saturated N,N′-substituted or N,N,N′,N′-substituted 1,3-propanediamines or are heated together with other amines, such that an amine exchange takes place. It is stated that amine exchange and hydrogenation can also be performed simultaneously in the presence of a Raney® nickel catalyst. Thus, a mixture of isopropylpropylamine and N-isopropyl-1,3-propanediamine was obtained in two stages, by, in the first stage, first reacting acrolein and isopropylamine, and, in a second stage, hydrogenating the resulting reaction mixture, after removal of excess amine and solvent, with ammonia in the presence of Raney® nickel at a temperature of 105° C. There is no indication that N,N-substituted 3-aminopropan-1-ols can be formed with high selectivity.